Image sensor device and method

ABSTRACT

A system and method for blocking heat from reaching an image sensor in a three dimensional stack with a semiconductor device. In an embodiment a heat sink is formed in a back end of line process either on the semiconductor device or else on the image sensor itself when the image sensor is in a backside illuminated configuration. The heat sink may be a grid in either a single layer or in two layers, a zig-zag pattern, or in an interleaved fingers configuration.

This application claims priority to U.S. Provisional Application No.61/791,989, filed on Mar. 15, 2013, and entitled “Image Sensor Deviceand Method,” which application is incorporated herein by reference.

BACKGROUND

Complementary metal oxide semiconductor image sensors generally utilizea series of photodiodes formed within an array of pixel regions of asemiconductor substrate in order to sense when light has impacted thephotodiode. Adjacent to each of the photodiodes within each of the pixelregions a transfer transistor may be formed in order to transfer thesignal generated by the sensed light within the photodiode at a desiredtime. Such photodiodes and transfer transistors allow for an image to becaptured at a desired time by operating the transfer transistor at thedesired time.

The complementary metal oxide semiconductor image sensors may generallybe formed in either a front side illumination configuration or aback-side illumination configuration. In a front-side illuminationconfiguration light passes to the photodiode from the “front” side ofthe image sensor where the transfer transistor has been formed. However,in this configuration the light is forced to pass through metal layers,dielectric layers, and past the transfer transistor before it reachesthe photodiode. This may generate processing and/or operational issuesas the metal layers, dielectric layers, and the transfer transistor maynot necessarily be transparent and may block the light as it is tryingto reach the photodiode.

In a back-side illumination configuration, the transfer transistor, themetal layers, and the dielectric layers are formed on the front side ofthe substrate, and light is allowed to pass to the photodiode from the“back” side of the substrate such that the light hits the photodiodebefore it reaches the transfer transistor, the dielectric layers, or themetal layers. Such a configuration may reduce the complexity of themanufacturing of the image sensor and its operation.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates an image sensor and an ASIC device in accordance withan embodiment;

FIGS. 2A-2D illustrate embodiments of a heat sink in accordance with anembodiment;

FIG. 3 illustrates a bonding of the image sensor and the ASIC device ina package in accordance with an embodiment;

FIG. 4 illustrates another packaging of the image sensor and the ASICdevice in accordance with an embodiment;

FIG. 5 illustrates a thermal resistance chart in accordance with anembodiment;

FIG. 6 illustrates an embodiment in which the heat sink is formed withinan image sensor in accordance with an embodiment; and

FIGS. 7A-7D illustrate other packages in which embodiments may beimplemented.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the embodiments andare not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of embodiments are discussed in detail below. Itshould be appreciated, however, that the embodiments provide manyapplicable concepts that can be embodied in a wide variety of specificcontexts. The specific embodiments discussed are merely illustrative ofspecific ways to make and use the embodiments, and do not limit thescope of the embodiments.

Embodiments will be described with respect to a specific context, namelya complementary metal oxide semiconductor (CMOS) back side illuminatedimage sensor in a three-dimensional stack. Other embodiments may also beapplied, however, to other image sensors and other semiconductor devicesin different packages.

With reference now to FIG. 1, there is shown an image sensor 100 whichcomprises a grid or array of backside illuminated pixels in a pixelregion 101. The backside illuminated pixels will receive light that hasimpacted upon the backside of the image sensor 100 and translate thatlight into an electrical impulse. In an embodiment the backsideilluminated pixels comprise a photosensitive diode along with, e.g., atransfer transistor, in order to receive light and transmit anelectrical signal.

The image sensor 100 also may comprise a logic region 103 locatedadjacent to the pixel region 101. The logic region 103 may haveadditional circuitry and contacts for input and output connections toand from the pixel region 101. The logic region 103 is utilized toprovide an operating environment for the pixel region 101 and tomoderate communications between the array of pixel region 101 and otherexternal devices such as a semiconductor device 120 (described furtherbelow).

The pixel region 101 and the logic region 103 may be formed in a firstsubstrate 105. The first substrate 105 may comprise a front side 107 anda back side 109 and may be a semiconductor material such as silicon,germanium, diamond, or the like, with a crystal orientation of (110).Alternatively, compound materials such as silicon germanium, siliconcarbide, gallium arsenic, indium arsenide, indium phosphide, silicongermanium carbide, gallium arsenic phosphide, gallium indium phosphide,combinations of these, and the like, with other crystal orientations,may also be used. Additionally, the first substrate 105 may comprise asilicon-on-insulator (SOI) substrate. Generally, an SOI substratecomprises a layer of a semiconductor material such as epitaxial silicon,germanium, silicon germanium, SOI, silicon germanium on insulator(SGOI), or combinations thereof. The first substrate 105 may be dopedwith a p-type dopant, such as boron, gallium, although the substrate mayalternatively be doped with an n-type dopant, as is known in the art.

Photosensitive diodes (not individually illustrated) may be formed inthe pixel region 101. The photosensitive diodes may be utilized togenerate a signal related to the intensity or brightness of light thatimpinges on the photosensitive diodes. In an embodiment thephotosensitive diodes may comprise n-type doped regions formed in thefirst substrate 105 (which in this embodiment may be a p-type substrate)and also may comprise heavily doped p-type doped regions formed on thesurface of the n-type doped regions to form a p-n-p junction.

The n-type doped regions may be formed, e.g., using a photolithographicmasking and implantation process. For example, a first photoresist (notshown in FIG. 1) may be placed on the first substrate 105. The firstphotoresist, may comprise a conventional photoresist material, such as adeep ultra-violet (DUV) photoresist, and may be deposited on the surfaceof the first substrate 105, for example, by using a spin-on process toplace the first photoresist. However, any other suitable material ormethod of forming or placing the first photoresist may alternatively beutilized. Once the first photoresist has been placed on the firstsubstrate 105, the first photoresist may be exposed to energy, e.g.light, through a patterned reticle in order to induce a reaction inthose portions of the first photoresist exposed to the energy. The firstphotoresist may then be developed, and portions of the first photoresistmay be removed, exposing a portion of the first substrate 105 where thephotosensitive diodes are desired to be located.

Once the first photoresist has been placed and developed, the heavilydoped n-type doped regions may be formed by implanting n-type dopants(e.g., phosphorous, arsenic, antimony, or the like) through the firstphotoresist. In an embodiment the n-type doped regions may be implantedsuch that their concentration of between about 1e15 atom/cm³ and about1e20 atom/cm³, such as about 8e15 atom/cm³. However, any suitablealternative concentration for the heavily doped n-type doped regions mayalternatively be utilized.

After the n-type doped regions have been formed (e.g., through theimplantation process), the p-type doped regions may be formed using,e.g., an ion implantation process using the first photoresist as a mask.The p-type doped regions may be formed to extend into the firstsubstrate 105 between about 1 μm and about 4 μm. Additionally, thep-type doped regions may be formed to have a concentration of betweenabout 1e15 atom/cm³ and about 5e19 atom/cm³, such as about 1e16atom/cm³.

Once the photosensitive diodes have been formed, the first photoresistmay be removed. In an embodiment, the first photoresist may be removedusing a process such as ashing. In such an embodiment a temperature ofthe first photoresist may be increased until the first photoresistundergoes a thermal decomposition, at which point the first photoresistmay be removed. However, any other suitable removal process mayalternatively be utilized to remove the first photoresist.

Further, as one of ordinary skill in the art will recognize, thephotosensitive diodes described above are merely one type ofphotosensitive diodes that may be used in the embodiments. Any suitablephotodiode may be utilized with the embodiments, and all of thesephotodiodes are intended to be included within the scope of theembodiments. Additionally, the precise methods or order of stepsdescribed above may be modified, such as by forming the p-type dopedregions prior to the formation of the n-type doped regions, while stillremaining within the scope of the embodiments.

A first transistor 111 may be formed in the pixel region 101 and asecond transistor 113 may be formed in the logic region 103. In anembodiment the first transistor 111 may be a transfer transistor.However, the first transistor 111 is also merely representative of themany types of functional transistors that may be utilized within thepixel region 101. For example, while the first transistor 111 in FIG. 1may be, e.g., a transfer transistor, embodiments may additionallyinclude other transistors located within the pixel region 101, such asreset transistors, source follower transistors, or select transistors.These transistors may be arranged, for example, to form a fourtransistor CMOS image sensor (CIS). All suitable transistors andconfigurations that may be utilized in an image sensor are fullyintended to be included within the scope of the embodiments. Similarly,while the second transistor 113 is illustrated in FIG. 1 as a logictransistor, it is also merely representative of the many types of activeand passive devices that may be formed in the logic region 103 in orderto provide the suitable connectivity to and from the pixel region 101.

The first transistor 111 and the second transistor 113 may comprise gatestacks that may be formed over the first substrate 105. The gate stacksmay each comprise a gate dielectric and a gate electrode. The gatedielectrics and gate electrodes may be formed and patterned on the firstsubstrate 105 by any suitable process known in the art. The gatedielectrics may be a high-K dielectric material, such as silicon oxide,silicon oxynitride, silicon nitride, an oxide, a nitrogen-containingoxide, aluminum oxide, lanthanum oxide, hafnium oxide, zirconium oxide,hafnium oxynitride, a combination thereof, or the like. The gatedielectrics may have a relative permittivity value greater than about 4.

In an embodiment in which the gate dielectrics comprise an oxide layer,the gate dielectrics may be formed by any oxidation process, such as wetor dry thermal oxidation in an ambient comprising an oxide, H₂O, NO, ora combination thereof, or by chemical vapor deposition (CVD) techniquesusing tetra-ethyl-ortho-silicate (TEOS) and oxygen as a precursor. Inone embodiment, the gate dielectrics may be between about 10 Å to about150 Å in thickness, such as 100 Å in thickness.

The gate electrodes may comprise a conductive material, such as a metal(e.g., tantalum, titanium, molybdenum, tungsten, platinum, aluminum,hafnium, ruthenium), a metal silicide (e.g., titanium silicide, cobaltsilicide, nickel silicide, tantalum silicide), a metal nitride (e.g.,titanium nitride, tantalum nitride), doped poly-crystalline silicon,other conductive materials, or a combination thereof. In one example,amorphous silicon is deposited and recrystallized to createpoly-crystalline silicon (poly-silicon). In an embodiment in which thegate electrodes is poly-silicon, the gate electrodes may be formed bydepositing doped or undoped poly-silicon by low-pressure chemical vapordeposition (LPCVD) to a thickness in the range of about 100 Å to about2,500 Å, such as 1,200 Å.

Spacers may be formed on the sidewalls of the gate dielectrics and thegate electrodes. The spacers may be formed by blanket depositing aspacer layer on the previously formed structure. The spacer layer maycomprise SiN, oxynitride, SiC, SiON, oxide, and the like, and may beformed by commonly used methods such as chemical vapor deposition (CVD),plasma enhanced CVD, sputter, and other methods known in the art. Thespacer layer is then patterned to form the spacers, such as byanisotropically etching to remove the spacer layer from the horizontalsurfaces of the structure.

Source/drain regions may be formed in the first substrate 105 on anopposing side of the gate dielectrics from the photosensitive diodes andalso on opposing sides of the gate stack of the second transistor 113.In an embodiment in which the first substrate 105 is a p-type substrate,the source/drain regions may be formed by implanting appropriate n-typedopants such as phosphorous, arsenic or antimony. The source/drainregions may be implanted using the gate electrodes and the spacers asmasks to form lightly doped source/drain (LDD) regions and heavily dopedsource/drain regions.

It should be noted that one of ordinary skill in the art will realizethat many other processes, steps, or the like may be used to form thesource/drain regions and the photosensitive diodes. For example, one ofordinary skill in the art will realize that a plurality of implants maybe performed using various combinations of spacers and liners to formthe source/drain regions and the photosensitive diodes having a specificshape or characteristic suitable for a particular purpose. Any of theseprocesses may be used to form the source/drain regions and thephotosensitive diodes, and the above description is not meant to limitthe embodiments to the steps presented above.

Once the first transistor 111 and the second transistor 113 have beenformed, a first inter-layer dielectric (ILD) layer 116 may be formedover the pixel region 101 and contacts (not individually illustrated)may be formed through the first ILD layer 116. The first ILD layer 116may comprise a material such as boron phosphorous silicate glass (BPSG),although any suitable dielectrics may be used for either layer. Thefirst ILD layer 116 may be formed using a process such as PECVD,although other processes, such as LPCVD, may alternatively be used. Thefirst ILD layer 116 may be formed to a thickness of between about 100 Åand about 3,000 Å.

Contacts (not individually illustrate in FIG. 1) may be formed throughthe first ILD layer 116 with suitable photolithography and etchingtechniques. In an embodiment a first photoresist material is utilized tocreate a patterned mask to define contacts. Additional masks, such as ahardmask, may also be used. An etching process, such as an anisotropicor isotropic etch process, is performed to etch the first ILD layer 116.

Contacts may then be formed so as to contact the first substrate 105 andthe gate electrodes. The contacts may comprise a barrier/adhesion layer(not individually shown in FIG. 1) to prevent diffusion and providebetter adhesion for the contacts. In an embodiment, the barrier layer isformed of one or more layers of titanium, titanium nitride, tantalum,tantalum nitride, or the like. The barrier layer may be formed throughchemical vapor deposition, although other techniques could alternativelybe used. The barrier layer may be formed to a combined thickness ofabout 50 Å to about 500 Å.

The contacts may be formed of any suitable conductive material, such asa highly-conductive, low-resistive metal, elemental metal, transitionmetal, or the like. In an exemplary embodiment the contacts are formedof tungsten, although other materials, such as copper, couldalternatively be utilized. In an embodiment in which the contacts areformed of tungsten, the contacts may be deposited by CVD techniquesknown in the art, although any method of formation could alternativelybe used.

After the contacts are formed, further processing of the front side 107of the first substrate 105 may be performed. This processing maycomprise various back-end-of-line processing such as forming variousconductive and dielectric layers in order to form interconnectionsbetween the individually formed devices to each other. Theseinterconnections may be made through any suitable formation process(e.g., lithography with etching, damascene, dual damascene, or the like)and may be formed using suitable conductive materials such as aluminumalloys, copper alloys, or the like.

Further processing may be performed on the back side 109 of the firstsubstrate 105 after the processing on the front side 107 of the firstsubstrate 105. In an embodiment the thickness of the back side 109 ofthe first substrate 105 may be reduced, or thinned. Thinning reduces thedistance that light travels through the back side 109 of the firstsubstrate 105 before it reaches the photosensitive diodes. The thinningof the back side 109 of the first substrate 105 may be performed using aremoval process such as chemical mechanical polishing (CMP). In a CMPprocess, a combination of etching materials and abrading materials areput into contact with the back side 109 of the first substrate 105 and agrinding pad (not shown) is used to grind away the back side 109 of thefirst substrate 105 until a desired thickness is achieved. However, anysuitable process for thinning the back side 109 of the first substrate105, such as etching or a combination of CMP and etching, mayalternatively be used. The back side 109 of the first substrate 105 maybe thinned so that the first substrate 105 has a thickness of betweenabout 2 μm and about 2.3 μm.

Once thinned, color filters 115 may be formed on the back side 109 ofthe first substrate 105. The color filters 115 may comprise filters forone of the primary colors (e.g., red, green, blue) and may be positionedto filter the light that will impinge upon the photosensitive diodes.The color filters 115 may be part of an array pattern of color filters,with each color filter being located over a respective pixel within thepixel region 101. For example, the color filters 115 may be part of aBayer RGB pattern, a Yotsuba CRGB pattern, or any other suitable patternfor the location of color filters 115 over the image sensor 100.

The color filters 115 may comprise a polymeric material or resin, suchas a polymeric polymer, which includes colored pigments. In anembodiment in which a polymeric polymer is utilized to form the colorfilters 115, the color filters 115 may be formed over the pixel region101 using a process such as spin coating to form a first blanket layerof the first polymeric polymer, although any other suitable method mayalternatively be utilized.

Once the first blanket layer of the polymeric polymer has been formed,the first blanket layer may be patterned such that the color filters 115are formed over the desired pixels in the pixel region 101. In anembodiment the first blanket layer may be patterned using a suitablephotolithographic masking and etching process, wherein a photoresist isplaced, exposed, and developed to cover the desired portions of thefirst blanket layer. Once the desired portions are protected, theexposed portions of the first blanket layer may be removed using, e.g.,an anisotropic etch. This process may be repeated for each desired colorto form an array of color filters 115.

Optionally, microlenses 118 may be formed over the color filters 115.The microlenses 118 may be used to focus impinging light more directlyonto the photosensitive diodes. The microlenses 118 may be formed byfirst applying and patterning a positive type photoresist (not shown)over the color filters 115. Once formed, the patterned photoresist maythen be baked to round the photoresist into the curved microlenses 118.

Also illustrated in FIG. 1 is a semiconductor device 120 that will bebonded to the image sensor 100. In an embodiment the semiconductordevice 120 is an ASIC device such as an image signal processor (ISP)that connects to the image sensor 100 in order to provide power andground to the image sensor 100. The semiconductor device 120 alsoreceives and/or sends signals to and from the image sensor 100,processes these signals, and may route the signals to external devices.

In an embodiment the semiconductor device 120 includes a secondsubstrate 121 with active devices 123, metallization layers 127 and aheat sink 129. The second substrate 121 may comprise bulk silicon, dopedor undoped, or an active layer of a silicon-on-insulator (SOI)substrate. Generally, an SOI substrate comprises a layer of asemiconductor material such as silicon, germanium, silicon germanium,SOI, silicon germanium on insulator (SGOI), or combinations thereof.Other substrates that may be used include multi-layered substrates,gradient substrates, or hybrid orientation substrates.

Active devices 123 may be formed on the second substrate 121. As one ofordinary skill in the art will recognize, a wide variety of activedevices such as capacitors, resistors, inductors and the like may beused to generate the desired structural and functional requirements ofthe design for the semiconductor device 120. The active devices 123 maybe formed using any suitable methods either within or else on thesurface of the second substrate 121.

The metallization layers 127 are formed over the second substrate 121and the active devices 123 and are designed to connect the variousactive devices 123 to form functional circuitry. While illustrated inFIG. 1 as a single layer, the metallization layers 127 may be formed ofalternating layers of dielectric (e.g., low-k dielectric material) andconductive material (e.g., copper) and may be formed through anysuitable process (such as deposition, damascene, dual damascene, etc.).In an embodiment there may be four layers of metallization separatedfrom the second substrate 121 by at least one interlayer dielectriclayer (ILD), but the precise number of metallization layers 127 isdependent upon the design of the semiconductor device 120.

The heat sink 129 is formed within the metallization layers 127. In anembodiment the heat sink 129 may act as a heat block and prevent heatgenerated from the semiconductor device 120 (e.g., the active devices123 on the second substrate 121) from reaching the image sensor 100 anddistorting or otherwise interfering with the image sensor 100. Forexample, if excess heat is allowed to reach the photodiodes within theimage sensor 100, the image quality or uniformity of images taken by theimage sensor 100 may be impacted. In particular examples, an improperheat distribution that could lead to a non-uniform image, and extra heatin the 3D stack of the image sensor 100 and the semiconductor device 120could worsen dark current/white pixel issues. In other words, improperheat distribution may cause a brighter image to occur at some parts ofthe image sensor 100 due to a higher temperature.

As such, the heat sink 129 may be formed as a way of blocking andrerouting the heat generated by the active devices 123. By placing theheat sink 129 between, e.g., the active devices 123 and the image sensor100, the heat sink 129 routes generated heat away from the image sensor100. In an embodiment the heat sink 129 may be formed as an additionalmetallization layer within the metallization layers 127 to ensure thatit is located between the active devices 123 and the image sensor 100,with the heat sink 129 shaped and formed to capture and reroute heataway from the image sensor 100.

Additionally, while illustrated in FIG. 1 as being within the upper mostlayer of the metallization layers 127, the embodiments are not limitedto this position. Rather, the heat sink 129 may be formed in anysuitable metallization layer or combination of metallization layerswithin the metallization layers 127. For example, the heat sink 129 maybe formed in a lower metallization layer while additional conductive andinsulative layers are formed on top of the heat sink 129. In such anembodiment connections and contacts (not individually illustrated) maybe routed through the heat sink 129 to electrically interconnect thevarious layers.

Alternatively, instead of forming an additional layer specifically forthe heat sink 129, which would add to the volume of the semiconductordevice 120, the heat sink 129 may be formed into an already existingmetallization layer such as by redesigning one of the existingmetallization layers to include the structure of the heat sink 129. Insuch an embodiment the metallization layer may be redesigned to providethe desired thermal routing in addition to the electrical routingwithout the need for an additional layer to be added to thesemiconductor device 120.

The heat sink 129 may be formed from thermally conductive material suchas a metal and may be made using similar processes as the formation andpatterning of the metallization layers 127. Such processes may includedeposition processes, plating processes (such as electroplating orelectroless plating processes), photolithographic masking and etchingprocesses, combinations of these or the like. Particular processes mayinclude damascene processes and dual damascene processes. In aparticular embodiment the heat sink 129 is formed from the samematerials as the conductive material within the metallization layers127, and may be made using the same processes and at the same time asthe metallization layers 127. As such, the inclusion of the heat sink129 is compatible with back-end-of-line technologies.

In a particular embodiment the heat sink 129 may comprise a metal suchas copper and may be formed using a damascene method of processing. Forexample, a dielectric material may be initially deposited over anunderlying layer using, e.g., a chemical vapor deposition process. Oncein place, a second photoresist (not individually illustrated) may beplaced, illuminated, and developed in order to expose portions of thedielectric material in those locations where the heat sink 129 isdesired. Once exposed, the dielectric material may be removed using,e.g., an etching process to form an opening in the dielectric material.After the etching process, the second photoresist may be removed using,e.g., a thermal process such as ashing.

After the second photoresist has been removed, the heat sink 129 may beformed using a first seed layer (not individually illustrated) and aplating process, such as electrochemical plating, although otherprocesses of formation, such as sputtering, evaporation, or PECVD, mayalternatively be used depending upon the desired materials. The heatsink 129 may comprise copper, but other thermally conductive materials,such as aluminum or tungsten, may alternatively be used. Once theopenings in the dielectric material have been filled with conductivematerial, any excess conductive material outside of the openings in thedielectric material may be removed, and the heat sink 129 may beplanarized with the dielectric material using, for example, a chemicalmechanical polishing process.

Formed along with the heat sink 129 in a same layer as the heat sink 129are horizontal portions of thermal vias 131 that connect to the heatsink 129 and allow for the desired routing of the heat away from theheat sink 129 (as discussed further below with respect to FIG. 3). In anembodiment the horizontal portions of thermal vias 131 may be formedeither in the same process as the heat sink 129 or else, if desired,separated processes such as dual damascene or other deposition andpatterning processes may be used to form the horizontal portions of thethermal vias 131.

FIGS. 2A-2D illustrate various embodiments of the heat sink 129. FIG. 2Aillustrates a single layer grid pattern heat sink in which a grid 201 ofconductive material is formed in a single layer of the metallizationlayers 127. The metal routing with the grid 201 of the heat sink 129helps to reduce the process complexity by using a wide area metal tohelp block heat while simultaneously providing a uniform heatdistribution. FIG. 2A additionally illustrates a path of heat transfer203 from the semiconductor device 120 to the heat sink 129 and thenthrough the heat sink 129 (illustrated using the arrows labeled 203 inFIG. 2A).

FIG. 2B illustrates a two layer grid pattern heat sink in which a firstlayer 205 of straight, parallel lines of the heat sink 129 is formed ina first layer of the metallization layers 127. Additionally in thisembodiment, a second layer 207 of straight, parallel lines of the heatsink 129 is formed in a second layer of the metallization layers 127over the first layer 205. By utilizing a multi-layer design for the heatsink 129, the heat sink 129 in this embodiment enhances thermaldissipation and heat blocking from the semiconductor device 120 byutilizing the second layer 207 to capture any residual heat that maypass through the first layer 205 of the heat sink 129.

FIG. 2C illustrates another embodiment of a pattern for the heat sink129. In this embodiment the heat sink 129 is arranged in a single layerand has a zigzag pattern. For example, the heat sink 129 in thisembodiment has a series of parallel lines 209 that are connected to eachother by cross-pieces 211 that alternate between one side of the heatsink 129 and the other side of the heat sink 129 to form a pattern thatcriss-crosses while allowing for the flow of heat through the heat sink129.

FIG. 2D illustrates yet another embodiment of a pattern for the heatsink 129. In this embodiment the heat sink 129 has multiple fingers 213offset from each other. Every other finger is connected by aperpendicular line 215, such that the combination of the multiplefingers and perpendicular lines 215 form a set of interleaved fingers.By utilizing two sets of fingers, multiple thermally conductive pathwaysmay be formed to enhance the ability of the heat to be removed beforereaching the image sensor 100.

FIG. 3 illustrates a bonding of the image sensor 100 and thesemiconductor device 120. In an embodiment the image sensor 100 and thesemiconductor device 120 may be bonded to each other using any suitablebonding technique, such as by oxide fusion bonding, silicon-on-glassbonding or the like. In an embodiment the fusion bonding may beperformed by initially forming an oxide layer on either one or both ofthe image sensor 100 or the semiconductor device 120. The oxide layermay be formed by a deposition process or, if the materials of the imagesensor 100 and semiconductor device 120 are suitable, exposing thesurfaces of the image sensor 100 and semiconductor device 120 to aoxidizing environment. Once formed, the image sensor 100 is then alignedwith the second substrate 121 and the two are contacted together toinitiate a bonding of the image sensor 100 with the second substrate121.

Once the bonding has been initiated by contacting the image sensor 100to the second substrate 121, the bonding process may be continued tostrengthen the bonding by heating the image sensor 100 and the secondsubstrate 121. In an embodiment this heating may be performed byannealing the image sensor 100 and the second substrate 121 at atemperature of between about 150° C. and about 800° C. in order tostrengthen the bond. However, any suitable method, including allowingthe image sensor 100 and the second substrate 121 to bond at roomtemperature, may alternatively be used, and all such bonding is fullyintended to be included within the scope of the embodiments.

Alternatively, a wet cleaning procedure may be utilized to initiate thefusion bond between the image sensor 100 and the second substrate 121.For example, in an embodiment in which the image sensor 100 is silicon,the image sensor 100 may be bonded by initially cleaning the imagesensor 100 using, e.g., a wet cleaning procedure such as an SC-1 or SC-2cleaning procedure to form a hydrophilic surface. The image sensor 100is then aligned with the second substrate 121 and the two are contactedtogether to begin the bonding procedure. Once the image sensor 100 hascontacted the second substrate 121, the thermal anneal may be utilizedto strengthen the bond.

In yet another embodiment, the image sensor 100 may be bonded by firsttreating the image sensor 100 to form a hydrophobic surface. Forexample, in an embodiment the image sensor 100 may etched using anetching solution of hydrogen fluoride (HF) or ammonium fluoride (NH₄F).Once treated, the image sensor 100 is then aligned with the secondsubstrate 121 and placed in contact. The contacted image sensor 100 andsecond substrate 121 are then annealed to strengthen the bond.

However, the descriptions of the fusion bonding using a oxide layer, acleaning process, or an etching solution as described above are merelyexamples of types of process that may be utilized in order to bond theimage sensor 100 to the second substrate 121, and are not intended to belimiting upon the embodiments. Rather, any suitable bonding process mayalternatively be utilized to bond the image sensor 100 to the secondsubstrate 121, and all such processes are fully intended to be includedwithin the embodiments.

FIG. 3 also illustrates the placing of the bonded image sensor 100 andthe semiconductor device 120 into a ceramic leadless chip carrier (CLCC)305. In this embodiment the semiconductor device 120 is attached to aprinted circuit board 301 using, e.g., an adhesion layer 303. Theadhesion layer 303 may comprise an adhesive material such as, e.g., aglue, an epoxy, a polymer, combinations of these, or the like, and maybe applied by initially applying an amount of the adhesive material tothe printed circuit board 301, placing the semiconductor device 120 incontact with the adhesion layer 303, and then curing the adhesion layer303 in order to solidify the connection between the printed circuitboard 301 and the semiconductor device 120.

In this embodiment vertical portions of thermal vias 313 may be formedthrough the image sensor 100 to the heat sink 129. These thermal vias313 may be, e.g., through substrate vias (TSVs) that connect to thehorizontal portions of the thermal vias 131 to form a path through theimage sensor 100 and the semiconductor device 120 to the heat sink 129.As such, the heat sink 129, the horizontal portions of the thermal vias131, and the vertical portions of the thermal vias 313, form a thermalpathway that removes heat from the semiconductor device 120 and routesheat away from the image sensor 100. By removing the heat from thesemiconductor device 120, the heat is removed before the heat can affectthe image sensor 100 and interfere with the operation of the imagesensor 100. As such, the heat sink 129 can make the overall packageddevice comprising the image sensor 100 and the semiconductor device 120more efficient.

In an embodiment the vertical portions of the thermal vias 313 may beformed after the image sensor 100 and the semiconductor device 120 havebeen bonded. For example, the vertical portions of the thermal vias 313may be formed using, e.g., a deep via type of technology to etch throughthe image sensor 100 and the semiconductor device 120 to the horizontalportion of the thermal via 131. Once the opening has been formed, theopening may be filled with a conductive material such as copper using,e.g., a seed layer followed by an electroplating process, although anysuitable process may alternatively be formed. Excess material outside ofthe opening may then be removed.

Alternatively, the formation of the vertical portion of the thermal via313 may be incorporated into the formation processes of the image sensor100 and the semiconductor device 120. For example, the vertical portionof the thermal via 313 may be formed within each of the individuallayers (e.g., the first ILD layer 116, the metallization layers 127,etc.) as these layers are being formed. Once these layers with theconnecting portions of the vertical portion of the thermal vias 313 havebeen formed, the image sensor 100 may be bonded to the semiconductordevice 120 such that the individual portions of the vertical portion ofthe thermal vias 313 are aligned with each other to provide a pathwayfrom the heat sink 129 through the image sensor 100.

However, while two processes for forming the vertical portions of thethermal vias 313 are described above, these processes are intended to beillustrative only and are not intended to be limiting upon theembodiments. Rather, any suitable processes or combination of processesmay alternatively be used to form the horizontal portions of the thermalvias 131 and the vertical portions of the thermal vias 313 and connectthe horizontal portions of the thermal vias 131 and the verticalportions of the thermal vias 313. All such processes are fully intendedto be included within the scope of the embodiments.

Once the horizontal portions of the thermal vias 131 and the verticalportions of the thermal vias 313 have been formed through thesemiconductor device 120 and the image sensor 100, an external connector315, such as a wire bond may be used to connect the vertical portions ofthe thermal vias 313 to the CLCC package 305. In an embodiment in whichthe external connector 315 is a wire bond, an electronic flame off (EFO)wand may be used to raise the temperature of a gold wire (notindividually illustrated in FIG. 3) within a capillary controlled by awire clamp (also not individually illustrated in FIG. 3). Once thetemperature of the gold wire is raised to between about 150° C. andabout 250° C., the gold wire is contacted to the image sensor 100 toform a first contact and then the gold wire is moved to a lead in theCLCC package 305 (also not individually illustrated in FIG. 3) to form asecond contact. Once connected, the remainder of the gold wire isseparated from the connected portions to form the external connector315.

However, as one of ordinary skill in the art will recognize, the wirebond embodiment for the external connectors 315 described above is notthe only type of electrical and physical connections that may be madebetween the image sensor 100 and the CLCC package 305. Rather, any othersuitable connection between the vertical portions of the thermal vias313 and the CLCC package 305 may alternatively be utilized, and all suchconnections are fully intended to be included within the scope of theembodiments.

Additionally, the CLCC package 305 may comprise glass 317 overlying thepixel region 101 of the image sensor 100 in order to provide protectionto the image sensor 100 while also allowing light to pass through to thepixels within the pixel region 101. An optical cover 319 may be placedover the glass 317 and the image sensor 100 in order to seal the CLCCpackage 305 and provide protection to the image sensor 100 and thesemiconductor device 120 from the external environment.

In this embodiment the heat sink, 129, the horizontal portions of thethermal vias 131, the vertical portions of the thermal vias 313, theexternal connector 315, and the CLCC package provide a thermal pathwayfor heat to travel around the photodiode within the image sensor 100. Byrouting heat along this path instead of into the pixel array of theimage sensor, deviations in images caused by undesired heat may beminimized or eliminated, thereby making the overall device moreefficient.

FIG. 4 illustrates another embodiment in which the bonded semiconductordevice 120 and image sensor 100 are packaged within a flip chip package400. In this embodiment, instead of physically attaching thesemiconductor device 120 to the printed circuit board 301, the imagesensor 100 is physically connected to the flip chip package 400 using,e.g., gold stud bumps (GSB) 401, although any other suitable method ofattachment may alternatively be utilized. In an embodiment in which GSBs401 are utilized, a non-conductive adhesive and underfill (notindividually illustrated in FIG. 4) are placed on the flip chip package400, and gold stud bumps are formed on the image sensor 100 inelectrical contact with the vertical portions of the thermal vias 313.Once the GSBs 401 are formed and the image sensor 100 has been alignedwith the flip chip package 400, pressure and heat are applied to crushthe GSBs 401 and force them through the non-conductive adhesive andunderfill to make contact with conductive traces (such as a coppernickel gold alloy trace, also not individually illustrated in FIG. 4) inthe flip chip package 400.

Accordingly, the vertical portions of the thermal vias 313, instead ofbeing connected to the external connectors 315, are in direct contactwith the flip chip (GSB) package 400 itself. As such, the heat sink 129,the horizontal portions of the thermal vias 131, the vertical portionsof the thermal vias 313 and the flip chip (GSB) package 400 itselfprovide a thermal path that removes heat from the semiconductor device120 before the heat can interfere with the image sensor 100.

FIG. 5 illustrates a thermal path 501 of heat being directed around theimage sensor 100. In the embodiment illustrated, the second substrate121 of the semiconductor device 120 is silicon (with a thermalconductivity of 149 W/(m*K)), the heat sink 129 is formed of copper(with a thermal conductivity of 401 W/(m*K)), and the image sensor 100and the semiconductor device 120 are bonded using a layer of silicondioxide 503 (with a thermal conductivity of 1.2-1.4 (W/(m*K)), which maybe about 1 μm in thickness. As such, heat generated by the semiconductordevice 120, instead of flowing through the layer of silicon dioxide 503of the bond with its low thermal conductivity, will instead flowprimarily through the copper in the heat sink 129, which has a muchhigher thermal conductivity. By utilizing the differences in thermalconductivity, the heat may be channeled along the thermal path 501 inthe heat sink 129 before it can significantly enter the image sensor 100through the layer of silicon dioxide 503.

FIG. 6 illustrates another alternative embodiment in which the heat sink129 is not formed within the semiconductor device 120. Rather, the heatsink 129 is formed in the metallization layers 117 of the image sensor100. For example, the heat sink 129 may be formed as one or more of thelayers during the back-end-of-line processing of the image sensor 100and, once the image sensor 100 has been bonded to the semiconductordevice 120, the heat sink 129 remains between the heat generation of thesemiconductor device 120 and the pixel region 101 of the image sensor100. In this embodiment the horizontal portions of the thermal vias 131and the vertical portions of the thermal vias 313 (in either embodimentdescribed above) may be formed to connect to the heat sink 129 in theimage sensor 100 rather than being formed through the image sensor 100and into the semiconductor device 120.

By forming the heat sink 129 between the active devices 123 and thepixel array of the image sensor, a uniform heat distribution below theimage sensor 100 may be generated to avoid any partial bright ornonuniform image issues that may arise from non-uniform heatdistribution. This helps to keep the image quality comparable to otherback-side illuminated CMOS image sensors that may not use thesemiconductor device 120.

FIGS. 7A-7D illustrate other packages that may be utilized with theembodiments to provide a thermal pathway away from the image sensor 100.For example, FIG. 7A illustrates a reconstructed wafer (RW) chip onboard (COB) package 701 which provides not only a package for the imagesensor 100 but also passive components 702 that may be used with theimage sensor 100. FIG. 7B illustrates a quad flat package (QFP) 703 withwire bonds, and FIG. 7C illustrates a chip scale package 705. Finally,FIG. 7D illustrates a through silicon via (TSV) type of package withcontrolled, collapse, chip connection (C4) connectors.

Additionally, in an embodiment in which a RW/COB package 701 isutilized, the process flow for a reconstructed wafer may involve aninitial quality control followed by wafer taping, wafer grinding, waferde-taping, wafer mounting, wafer sawing, and a first AVI inspection.Once the first AVI inspection has been performed, a UV irradiation maybe performed, followed by a die sort, a deionized water cleaning, asecond AVI inspection, a 100% visual inspection by 60× opticalmicroscope, a quality assurance gate, a 100% AOI check, and anotherquality assurance gate before additional processing is performed. Suchprocessing allows for a reconstructed wafer with 100% known good dies onit for further processing.

However, as one of ordinary skill in the art will recognize, the twopackages described above with respect to FIGS. 3-4 are merelyrepresentative examples of packages into which embodiments may beutilized. Rather, any other suitable package technology mayalternatively be utilized, and all such packages are fully intended tobe included within the scope of the embodiments.

By utilizing the heat sink 129 along with the heat conduction path(e.g., the horizontal portions of the thermal vias 131 and the verticalportions of the thermal vias 313), the external connectors 315 (or theGSBs 401), and the package itself (e.g., the CLCC package 305, theoverall heat dissipation of the full CIS chip can be reduced, whichdecreases the thermal budget in the chip. This allows for a more uniformheat distribution, which again lowers the thermal budget and allows fora better thermal dissipation. Such improvements allow for a moreefficient image sensor and an overall better product.

In accordance with an embodiment, a semiconductor device comprising animage sensor comprising a pixel is provided. A semiconductor device isbonded to the image sensor, the semiconductor device comprising asubstrate, and a heat sink is at least partially located in a firstmetallization layer between the pixel and the substrate.

In accordance with another embodiment, a semiconductor device comprisingan image sensor, the image sensor comprising a first substrate and afirst set of metallization layers adjacent to the first substrate isprovided. A semiconductor device is bonded to the image sensor, thesemiconductor device comprising active devices on a second substrate anda second set of metallization layers adjacent to the second substrate,the second set of metallization layers being different from the firstset of metallization layers, the first set of metallization layers andthe second set of metallization layers forming a third set ofmetallization layers between the first substrate and the secondsubstrate. A heat sink is located at least partially in the third set ofmetallization layers and a package is surrounding the image sensor andthe semiconductor device, the package in thermal connection with theheat sink.

In accordance with yet another embodiment, a method of manufacturing asemiconductor device comprising manufacturing a first semiconductordevice is provided. The manufacturing the first semiconductor devicecomprises forming active devices on a first substrate and forming aplurality of metallization layers over the active devices, the pluralityof metallization layers comprising a heat sink. The first semiconductordevice is bonded to an image sensor with the heat sink between theactive devices and the image sensor.

Although the present embodiments and their advantages have beendescribed in detail, it should be understood that various changes,substitutions and alterations can be made herein without departing fromthe spirit and scope of the embodiments as defined by the appendedclaims. For example, charge coupled devices (CCD) may be utilized inplace of the CMOS devices within the image sensor. These devices, stepsand materials may be varied while remaining within the scope of theembodiments.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the embodiments, processes, machines,manufacture, compositions of matter, means, methods, or steps, presentlyexisting or later to be developed, that perform substantially the samefunction or achieve substantially the same result as the correspondingembodiments described herein may be utilized according to theembodiments. Accordingly, the appended claims are intended to includewithin their scope such processes, machines, manufacture, compositionsof matter, means, methods, or steps.

What is claimed is:
 1. A semiconductor device comprising: an imagesensor comprising a pixel; a semiconductor device bonded to the imagesensor, the semiconductor device comprising a substrate; a heat sink atleast partially located in a first metallization layer between the pixeland the substrate; and a thermal via extending through the image sensor,the thermal via in thermal connection with the heat sink.
 2. Thesemiconductor device of claim 1, wherein the first metallization layeris part of the semiconductor device.
 3. The semiconductor device ofclaim 1, wherein the first metallization layer is part of the imagesensor.
 4. The semiconductor device of claim 1, further comprising aceramic leadless chip carrier package attached to the semiconductordevice and the image sensor.
 5. The semiconductor device of claim 1,further comprising a flip chip package attached to the semiconductordevice and the image sensor.
 6. The semiconductor device of claim 1,wherein the heat sink comprises a grid of thermally conductive materialin a single layer.
 7. The semiconductor device of claim 1, wherein theheat sink has a first portion located in the first metallization layerand a second portion located in a second metallization layer.
 8. Thesemiconductor device of claim 1, wherein the heat sink is in a zigzagpattern.
 9. The semiconductor device of claim 1, wherein the heat sinkcomprises interleaved fingers.
 10. A semiconductor device comprising: animage sensor having a first side and a second side opposite the firstside, the image sensor comprising: a first substrate; a first set ofmetallization layers adjacent to the first substrate; and a firstthermal via extending from the first side to the second side; asemiconductor device bonded to the image sensor, the semiconductordevice comprising: active devices on a second substrate; a second set ofmetallization layers adjacent to the second substrate, the second set ofmetallization layers being different from the first set of metallizationlayers, the first set of metallization layers and the second set ofmetallization layers forming a third set of metallization layers betweenthe first substrate and the second substrate; and a second thermal vialocated in the second set of metallization layers, the second thermalvia in thermal connection with the first thermal via; a heat sinklocated at least partially in the third set of metallization layers, theheat sink in thermal connection with the second thermal via; and apackage surrounding the image sensor and the semiconductor device, thepackage in thermal connection with the first thermal via.
 11. Thesemiconductor device of claim 10, wherein the heat sink is at leastpartially in the first set of metallization layers.
 12. Thesemiconductor device of claim 10, wherein the heat sink is at leastpartially in the second set of metallization layers.
 13. Thesemiconductor device of claim 10, wherein the package is a ceramicleadless chip carrier package.
 14. The semiconductor device of claim 10,wherein the package is a flip chip package.
 15. A method ofmanufacturing a semiconductor device, the method comprising:manufacturing a first semiconductor device, the manufacturing the firstsemiconductor device comprising: forming active devices on a firstsubstrate; and forming a plurality of metallization layers over theactive devices, the plurality of metallization layers comprising a heatsink; and bonding the first semiconductor device to an image sensor withthe heat sink between the active devices and the image sensor; andforming a thermal via through the image sensor, wherein the heat sinkand the thermal via form a thermal pathway through the image sensor andat least partially through the first semiconductor device.
 16. Themethod of claim 15, wherein the bonding the first semiconductor deviceto the image sensor is performed at least in part with a fusion bondingprocess.
 17. The method of claim 15, further comprising forming aconductive via in the plurality of metallization layers, the conductivevia being thermally coupled to the heat sink.
 18. The method of claim15, further comprising packaging the image sensor and the firstsemiconductor device with a ceramic leadless chip carrier.
 19. Themethod of claim 15, further comprising packaging the image sensor andthe first semiconductor device with a flip chip package.
 20. Thesemiconductor device of claim 1, further comprising a second thermal vialocated in the first metallization layer, the second thermal via inthermal connection with the heat sink.